class Solution {
    public int missingNumber(int[] nums) {
        int low = 0;
        int high = nums.length-1;
        while(low<=high){
            int mid = low + (high-low)/2;
            if(nums[mid]==mid){
                low = mid + 1;
            } else {
                high = mid - 1;
            }
        }
        return low;
    }
}

